Calcium, free radicals, and excitotoxic neuronal death in primary cell culture

Fluorescent probes for neuroscience: imaging ex vivo brain tissue sections

Neurobiological research relies heavily on imaging techniques, such as fluorescence microscopy, to understand neurological function and disease processes. However, the number and variety of fluorescent probes available for ex vivo tissue section imaging limits the advance of research in the field. In this review, we outline the current range of fluorescent probes that are available to researchers for ex vivo brain section imaging, including their physical and chemical characteristics, staining targets, and examples of discoveries for which they have been used. This review is organised into sections based on the biological target of the probe, including subcellular organelles, chemical species (e.g., labile metal ions), and pathological phenomenon (e.g., degenerating cells, aggregated proteins). We hope to inspire further development in this field, given the considerable benefits to be gained by the greater availability of suitably sensitive probes that have specificity for important brain tissue targets.

The role of mitochondrial uncoupling in the regulation of mitostasis after traumatic brain injury

Mitostasis, the maintenance of healthy mitochondria, plays a critical role in brain health. The brain's high energy demands and reliance on mitochondria for energy production make mitostasis vital for neuronal function. Traumatic brain injury (TBI) disrupts mitochondrial homeostasis, leading to secondary cellular damage, neuronal degeneration, and cognitive deficits. Mild mitochondrial uncoupling, which dissociates ATP production from oxygen consumption, offers a promising avenue for TBI treatment. Accumulating evidence, from endogenous and exogenous mitochondrial uncoupling, suggests that mitostasis is closely regulating by mitochondrial uncoupling and cellular injury environments may be more sensitive to uncoupling. Mitochondrial uncoupling can mitigate calcium overload, reduce oxidative stress, and induce mitochondrial proteostasis and mitophagy, a process that eliminates damaged mitochondria. The interplay between mitochondrial uncoupling and mitostasis is ripe for further investigation in the context of TBI. These multi-faceted mechanisms of action for mitochondrial uncoupling hold promise for TBI therapy, with the potential to restore mitochondrial health, improve neurological outcomes, and prevent long-term TBI-related pathology.

The smoothened agonist SAG reduces mitochondrial dysfunction and neurotoxicity of frataxin-deficient astrocytes

BACKGROUND

Friedreich's ataxia is a rare hereditary neurodegenerative disease caused by decreased levels of the mitochondrial protein frataxin. Similar to other neurodegenerative pathologies, previous studies suggested that astrocytes might contribute to the progression of the disease. To fully understand the mechanisms underlying neurodegeneration in Friedreich's ataxia, we investigated the reactivity status and functioning of cultured human astrocytes after frataxin depletion using an RNA interference-based approach and tested the effect of pharmacologically modulating the SHH pathway as a novel neuroprotective strategy.

RESULTS

We observed loss of cell viability, mitochondrial alterations, increased autophagy and lipid accumulation in cultured astrocytes upon frataxin depletion. Besides, frataxin-deficient cells show higher expression of several A1-reactivity markers and release of pro-inflammatory cytokines. Interestingly, most of these defects were prevented by chronically treating the cells with the smoothened agonist SAG. Furthermore, in vitro culture of neurons with conditioned medium from frataxin-deficient astrocytes results in a reduction of neuronal survival, neurite length and synapse formation. However, when frataxin-deficient astrocytes were chronically treated with SAG, we did not observe these alterations in neurons.

CONCLUSIONS

Our results demonstrate that the pharmacological activation of the SHH pathway could be used as a target to modulate astrocyte reactivity and neuron-glia interactions to prevent neurodegeneration in Friedreich's ataxia.

Co-Delivery of Docosahexaenoic Acid and Brain-Derived Neurotropic Factor from Electrospun Aligned Core-Shell Fibrous Membranes in Treatment of Spinal Cord Injury

To restore lost functions while repairing the neuronal structure after spinal cord injury (SCI), pharmacological interventions with multiple therapeutic agents will be a more effective modality given the complex pathophysiology of acute SCI. Toward this end, we prepared electrospun membranes containing aligned core-shell fibers with a polylactic acid (PLA) shell, and docosahexaenoic acid (DHA) or a brain-derived neurotropic factor (BDNF) in the core. The controlled release of both pro-regenerative agents is expected to provide combinatory treatment efficacy for effective neurogenesis, while aligned fiber topography is expected to guide directional neurite extension. The in vitro release study indicates that both DHA and BDNF could be released continuously from the electrospun membrane for up to 50 days, while aligned microfibers guide the neurite extension of primary cortical neurons along the fiber axis. Furthermore, the PLA/DHA/BDNF core-shell fibrous membrane (CSFM) provides a significantly higher neurite outgrowth length from the neuron cells than the PLA/DHA CSFM. This is supported by the upregulation of genes associated with neuroprotection and neuroplasticity from RT-PCR analysis. From an in vivo study by implanting a drug-loaded CSFM into the injury site of a rat suffering from SCI with a cervical hemisection, the co-delivery of DHA and BDNF from a PLA/DHA/BDNF CSFM could significantly improve neurological function recovery from behavioral assessment, as well as provide neuroprotection and promote neuroplasticity changes in recovered neuronal tissue from histological analysis.

DNA repair pathways are altered in neural cell models of frataxin deficiency

Friedreich's ataxia (FRDA) is a hereditary and predominantly neurodegenerative disease caused by a deficiency of the protein frataxin (FXN). As part of the overall efforts to understand the molecular basis of neurodegeneration in FRDA, a new human neural cell line with doxycycline-induced FXN knockdown was established. This cell line, hereafter referred to as iFKD-SY, is derived from the human neuroblastoma SH-SY5Y and retains the ability to differentiate into mature neuron-like cells. In both proliferating and differentiated iFKD-SY cells, the induction of FXN deficiency is accompanied by increases in oxidative stress and DNA damage, reduced aconitase enzyme activity, higher levels of p53 and p21, activation of caspase-3, and subsequent apoptosis. More interestingly, FXN-deficient iFKD-SY cells exhibit an important transcriptional deregulation in many of the genes implicated in DNA repair pathways. The levels of some crucial proteins involved in DNA repair appear notably diminished. Furthermore, similar changes are found in two additional neural cell models of FXN deficit: primary cultures of FXN-deficient mouse neurons and human olfactory mucosa stem cells obtained from biopsies of FRDA patients. These results suggest that the deficiency of FXN leads to a down-regulation of DNA repair pathways that synergizes with oxidative stress to provoke DNA damage, which may be involved in the pathogenesis of FRDA. Thus, a failure in DNA repair may be considered a shared common molecular mechanism contributing to neurodegeneration in a number of hereditary ataxias including FRDA.

Cryptotanshinone reduces neurotoxicity induced by cerebral ischemia-reperfusion injury involving modulation of microglial polarization

BACKGROUND

The diterpenoid cryptotanshinone (CTS) has wide biological functions, including inhibition of tumor growth, inflammation and apoptosis. The present study aimed to explore the possible effect of CTS on cerebral ischemia/reperfusion (I/R) injury and the underlying mechanisms.

METHODS

Male C57BL/6J mice underwent transient middle cerebral artery occlusion (tMCAO) and murine microglia BV2 cells were challenged by Oxygen/glucose deprivation, to mimic I/R and ischemic/hypoxic and reperfusion (H/R) injury, respectively. CTS was administered 0.5 h (10 mg/kg) after the onset of MCAO or 2 h (20μM) post OGD. Infarct volume and neurological deficit were measured. Immunofluorescence, qPCR, and western blot, were performed to detect the expression of cytokines, apoptotic marker, and M1/M2 phenotype-specific genes. Flow cytometry was applied for M1/M2 subpopulation or Annexin V/PI apoptosis assessment.

RESULTS

CTS significantly reduced cerebral infarct volume, neurologic deficit scores, pro-inflammatory cytokine production (IL-6, TNF-α, and IL-1β), apoptotic protein expression (cleaved caspase-3) of mice after tMCAO challenge. Furthermore, CTS attenuated CD16+ M1-type and elevated CD206+ M2-type microglia in vivo or in vitro.

CONCLUSIONS

We propose that the neuroprotective effect of CTS in the I/R or H/R context are explained modulation of microglial polarization, suggesting therapeutic potential for cerebral ischemic stroke.

βOHB Protective Pathways in Aralar-KO Neurons and Brain: An Alternative to Ketogenic Diet

Aralar/AGC1/Slc25a12, the mitochondrial aspartate-glutamate carrier expressed in neurons, is the regulatory component of the NADH malate-aspartate shuttle. AGC1 deficiency is a neuropediatric rare disease characterized by hypomyelination, hypotonia, developmental arrest, and epilepsy. We have investigated whether β-hydroxybutyrate (βOHB), the main ketone body (KB) produced in ketogenic diet (KD), is neuroprotective in aralar-knock-out (KO) neurons and mice. We report that βOHB efficiently recovers aralar-KO neurons from deficits in basal-stimulated and glutamate-stimulated respiration, effects requiring βOHB entry into the neuron, and protects from glutamate excitotoxicity. Aralar-deficient mice were fed a KD to investigate its therapeutic potential early in development, but this approach was unfeasible. Therefore, aralar-KO pups were treated without distinction of gender with daily intraperitoneal injections of βOHB during 5 d. This treatment resulted in a recovery of striatal markers of the dopaminergic system including dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC)/DA ratio, and vesicular monoamine transporter 2 (VMAT2) protein. Regarding postnatal myelination, myelin basic protein (MBP) and myelin-associated glycoprotein (MAG) myelin proteins were markedly increased in the cortices of βOHB-treated aralar-KO mice. Although brain Asp and NAA levels did not change by βOHB administration, a 4-d βOHB treatment to aralar-KO, but not to control, neurons led to a substantial increase in Asp (3-fold) and NAA (4-fold) levels. These results suggest that the lack of increase in brain Asp and NAA is possibly because of its active utilization by the aralar-KO brain and the likely involvement of neuronal NAA in postnatal myelination in these mice. The effectiveness of βOHB as a therapeutic treatment in AGC1 deficiency deserves further investigation.SIGNIFICANCE STATEMENT Aralar deficiency induces a fatal phenotype in humans and mice and is associated with impaired neurodevelopment, epilepsy, and hypomyelination. In neurons, highly expressing aralar, its deficiency causes a metabolic blockade hampering mitochondrial energetics and respiration. Here, we find that βOHB, the main metabolic product in KD, recovers defective mitochondrial respiration bypassing the metabolic failure in aralar-deficient neurons. βOHB oxidation in mitochondria boosts the synthesis of cytosolic aspartate (Asp) and NAA, which is impeded by aralar deficiency, presumably through citrate-malate shuttle. In aralar-knock-out (KO) mice, βOHB recovers from the drastic drop in specific dopaminergic and myelin markers. The βOHB-induced myelin synthesis occurring together with the marked increment in neuronal NAA synthesis supports the role of NAA as a lipid precursor during postnatal myelination.

Altered Secretome and ROS Production in Olfactory Mucosa Stem Cells Derived from Friedreich's Ataxia Patients

Friedreich’s ataxia is the most common hereditary ataxia for which there is no cure or approved treatment at present. However, therapeutic developments based on the understanding of pathological mechanisms underlying the disease have advanced considerably, with the implementation of cellular models that mimic the disease playing a crucial role. Human olfactory ecto-mesenchymal stem cells represent a novel model that could prove useful due to their accessibility and neurogenic capacity. Here, we isolated and cultured these stem cells from Friedreich´s ataxia patients and healthy donors, characterizing their phenotype and describing disease-specific features such as reduced cell viability, impaired aconitase activity, increased ROS production and the release of cytokines involved in neuroinflammation. Importantly, we observed a positive effect on patient-derived cells, when frataxin levels were restored, confirming the utility of this in vitro model to study the disease. This model will improve our understanding of Friedreich´s ataxia pathogenesis and will help in developing rationally designed therapeutic strategies.

Astrocyte- and Neuron-Derived Extracellular Vesicles from Alzheimer's Disease Patients Effect Complement-Mediated Neurotoxicity

We have previously shown that blood astrocytic-origin extracellular vesicles (AEVs) from Alzheimer’s disease (AD) patients contain high complement levels. To test the hypothesis that circulating EVs from AD patients can induce complement-mediated neurotoxicity involving Membrane Attack Complex (MAC) formation, we assessed the effects of immunocaptured AEVs (using anti-GLAST antibody), in comparison with neuronal-origin (N)EVs (using anti-L1CAM antibody), and nonspecific CD81+ EVs (using anti-CD81 antibody), from the plasma of AD, frontotemporal lobar degeneration (FTLD), and control participants. AEVs (and, less effectively, NEVs) of AD participants induced Membrane Attack Complex (MAC) expression on recipient neurons (by immunohistochemistry), membrane disruption (by EthD-1 assay), reduced neurite density (by Tuj-1 immunohistochemistry), and decreased cell viability (by MTT assay) in rat cortical neurons and human iPSC-derived neurons. Demonstration of decreased cell viability was replicated in a separate cohort of autopsy-confirmed AD patients. These effects were not produced by CD81+ EVs from AD participants or AEVs/NEVs from FTLD or control participants, and were suppressed by the MAC inhibitor CD59 and other complement inhibitors. Our results support the stated hypothesis and should motivate future studies on the roles of neuronal MAC deposition and AEV/NEV uptake, as effectors of neurodegeneration in AD.

Enhanced Production of Herpes Simplex Virus 1 Amplicon Vectors by Gene Modification and Optimization of Packaging Cell Growth Medium

Herpes simplex virus 1 (HSV-1)-derived amplicon vectors are unique in their ability to accommodate large DNA molecules allowing whole genomic loci to be included with all of their regulatory elements. Additional advantages of these amplicons include their minimal toxicity and ability to persist as episomes, with negligible risk of insertional mutagenesis, being particularly well-suited for gene therapy of neurological disorders due to their outstanding ability to deliver genes into neurons and other neural cells. However, extensive gene therapy application has been hindered by difficulties in vector production. This work improved HSV-1 amplicons production by genetic modification of the packaging cell line and optimization of the culture medium. A stably-transfected Vero 2-2 cell line overexpressing the anti-apoptotic Bcl-2 protein was generated, exhibiting an increased resistance to apoptosis, prolonged culture duration, and a significant improvement in viral vector production. Additionally, supplementation of the growth medium with antioxidants, polyamines, amino acids, and reduced glutathione further increased the yield of packaged amplicon vectors. With these modifications, HSV-1 amplicons could be isolated from culture supernatants instead of cell lysates, leading to vector preparations with higher titer and purity and paving the way for generation of stable cell lines that are capable of continuous herpesviral vector production.

Effect of naturally occurring α-synuclein-antibodies on toxic α-synuclein-fragments

Alpha-synuclein (α-Syn) is a soluble protein primarily expressed in presynaptic terminals in the central nervous system (CNS). Aggregates of fibrillated α-Syn are the major component of Lewy bodies (LB), a pathologic hallmark of idiopathic Parkinson's disease (PD). Recently, naturally occurring autoantibodies against human α-Syn (nAbs α-Syn) were detected in the peripheral blood of PD patients and controls. Here, we investigated the inhibitory effects of nAbs α-Syn on distinct α-Syn fragments, as well as inflammatory responses and cytotoxicity evoked by nAbs α-Syn in primary microglia. All α-Syn fragments induced the release of the pro-inflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) from microglia in primary culture. Cotreatment with nAbs α-Syn alleviated the release of pro-inflammatory cytokines induced by α-Syn fragments α-Syn 1-95, α-Syn 61-140, α-Syn 96-140 and α-Syn 112. Treatment with the α-Syn fragments α-Syn 1-95, α-Syn 61-140 and α-Syn 112 impaired the viability of primary microglia. This effect could not be counteracted by cotreatment with nAbs α-Syn. Data suggest an important role of nAbs α-Syn in the α-Syn-induced inflammation cascade, and indicate the potential importance of nAbs in the pathogenesis of PD. This could provide an experimental therapeutic target for patients with PD.

Protective role of phenylethanoid glycosides, Torenoside B and Savatiside A, in Alzheimer's disease

The current study assessed the efficacy of two phenylethanoid glycosides (PhGs), Torenoside B (TB) and Savatiside A (SA), in the treatment of Alzheimer's disease (AD). The effects of TB and SA compounds were first assessed following amyloid beta (Aβ)_25-35 induction in SH-SY5Y cells at a range of concentrations. Their effects on cell viability and reactive oxygen species (ROS) were determined by performing MTT and dichlorofluorescin diacetate assays, respectively. The concentration of intracellular Ca²⁺ was determined using Fluo-3AM to stain SH-SY5Y cells. SA and TB treatments were also assessed in Aβ_25-35-induced mice. Y-maze and Morris water maze methods were utilized to assess murine learning and memory capability. The pathological changes of murine hippocampi was determined using H&E and Nissl staining. In addition, biochemical parameters associated with intracellular reactive oxygen pathways including Maleic dialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), acetylcholinesterase (AChE) and Calnexin were also assessed. TB and SA treatment in Aβ_25-35-induced SH-SY5Y cells resulted in the restoration of cell morphology, an increase of SOD and GSH-Px activity, a decrease in ROS, Ca²⁺ and MDA content, and a decrease in Calnexin expression. Furthermore, SA or TB treatment administered to Aβ_25-35-induced mice improved their spatial/non-spatial learning and memory capabilities. The efficacy of treatment was also supported by a marked change in the morphological structure of pyramidal neurons in the CA1 areas of murine hippocampi, as well as an increase of SOD and GSH-Px activity. Treatment also resulted in a decrease in MDA content, AchE activity and Calnexin expression in murine hippocampal tissue. As potential AD treatment drugs, SA and TB compounds have been demonstrated to alleviate the oxidative stress induced by Aβ_25-35 via the regulation of intracellular calcium homeostasis and Calnexin, preventing AD development.

Ligustrazin increases lung cell autophagy and ameliorates paraquat-induced pulmonary fibrosis by inhibiting PI3K/Akt/mTOR and hedgehog signalling via increasing miR-193a expression

Background

Reactive oxygen species (ROS) levels largely determine pulmonary fibrosis. Antioxidants have been found to ameliorate lung fibrosis after long-term paraquat (PQ) exposure. The effects of antioxidants, however, on the signalling pathways involved in PQ-induced lung fibrosis have not yet been investigated sufficiently. Here, we examined the impacts of ligustrazin on lung fibrosis, in particular ROS-related autophagy and pro-fibrotic signalling pathways, using a murine model of PQ-induced lung fibrosis.

Methods

We explored the effects of microRNA-193 (miR-193a) on Hedgehog (Hh) and PI3K/Akt/mTOR signalling and oxidative stress in lung tissues. Levels of miR-193a, protein kinase B (Akt), phosphoinositide 3-Kinase (PI3K), ceclin1, mammalian target of rapamycin (mTOR), sonic hedgehog (SHH), myosin-like Bcl2 interacting protein (LC3), smoothened (Smo), and glioma-associated oncogene-1 (Gli-1) mRNAs were determined with quantitative real-time PCR. Protein levels of PI3K, p-mTOR, p-Akt, SHH, beclin1, gGli-1, LC3, smo, transforming growth factor-β1 (TGF-β1), mothers against DPP homologue-2 (Smad2), connective tissue growth factor (CTGF), collagen I, collagen III, α-smooth muscle actin (α-SMA) nuclear factor erythroid 2p45-related factor-2 (Nrf2), and p-Smad2 were detected by western blotting. In addition, α-SMA, malondialdehyde, ROS, superoxide dismutase (SOD), oxidised and reduced glutathione, hydroxyproline, and overall collagen levels were identified in lung tissues using immunohistochemistry.

Results

Long-term PQ exposure blocked miR-193a expression, reduced PI3K/Akt/mTOR signalling, increased oxidative stress, inhibited autophagy, increased Hh signalling, and facilitated the formation of pulmonary fibrosis. Ligustrazin blocked PI3K/Akt/mTOR and Hh signalling as well as reduced oxidative stress via increasing miR-193a expression and autophagy, all of which reduced pulmonary fibrosis. These effects of ligustrazin were accompanied by reduced TGF-β1, CTGF, and Collagen I and III expression.

Conclusions

Ligustrazin blocked PQ-induced PI3K/Akt/mTOR and Hh signalling by increasing miR-193a expression, thereby attenuating PQ-induced lung fibrosis.

Delayed epidural transplantation of human induced pluripotent stem cell-derived neural progenitors enhances functional recovery after stroke

Induced pluripotent stem cell-derived neural progenitor cells (iPSC-NPCs) are a promising source of tailor-made cell therapy for neurological diseases. However, major obstacles to clinical use still exist. To circumvent complications related to intracerebral administration, we implanted human iPSC-NPCs epidurally over the peri-infarct cortex 7 days after permanent middle cerebral artery occlusion in adult rats. Compared to controls, cell-treated rats showed significant improvements in paretic forelimb usage and grip strength from 10 days post-transplantation (dpt) onwards, as well as reductions in lesion volumes, inflammatory infiltration and astrogliosis at 21 dpt. Few iPSC-NPCs migrated into rat peri-infarct cortices and exhibited poor survival in tissue. To examine the paracrine therapeutic mechanisms of epidural iPSC-NPC grafts, we used transmembrane co-cultures of human iPSC-NPCs with rat cortical cells subjected to oxygen-glucose deprivation. Compared to other human stem cells, iPSC-NPCs were superior at promoting neuronal survival and outgrowth, and mitigating astrogliosis. Using comparative whole-genome microarrays and cytokine neutralization, we identified a neurorestorative secretome from iPSC-NPCs, and neutralizing enriched cytokines abolished neuroprotective effects in co-cultures. This proof-of-concept study demonstrates a relatively safe, yet effective epidural route for delivering human iPSC-NPCs, which acts predominately through discrete paracrine effects to promote functional recovery after stroke.

Extracellular Vesicle-Associated Aβ Mediates Trans-Neuronal Bioenergetic and Ca2+-Handling Deficits in Alzheimer's Disease Models

Alzheimer's Disease (AD) is an age-related neurodegenerative disorder in which aggregation-prone neurotoxic amyloid β-peptide (Aβ) accumulates in the brain. Extracellular vesicles (EVs) are small 50-150 nanometer membrane vesicles that have recently been implicated in the prion-like spread of self-aggregating proteins. Here we report that EVs isolated from AD patient CSF and plasma, from the plasma of two AD mouse models, and from the medium of neural cells expressing familial AD presenilin 1 mutations, destabilize neuronal Ca2+ homeostasis, impair mitochondrial function, and sensitize neurons to excitotoxicity. EVs contain a relatively low amount of Aβ but have an increased Aβ42/ Aβ40 ratio; the majority of Aβ is located on the surface of the EVs. Impairment of lysosome function results in increased generation EVs with elevated Aβ42 levels. EVs may mediate transcellular spread of pathogenic Aβ species and that impair neuronal Ca2+ handling and mitochondrial function, and may thereby render neurons vulnerable to excitotoxicity.

L-Lactate-Mediated Neuroprotection against Glutamate-Induced Excitotoxicity Requires ARALAR/AGC1

ARALAR/AGC1/Slc25a12, the aspartate-glutamate carrier from brain mitochondria, is the regulatory step in the malate-aspartate NADH shuttle, MAS. MAS is used to oxidize cytosolic NADH in mitochondria, a process required to maintain oxidative glucose utilization. The role of ARALAR was analyzed in two paradigms of glutamate-induced excitotoxicity in cortical neurons: glucose deprivation and acute glutamate stimulation. ARALAR deficiency did not aggravate glutamate-induced neuronal death in vitro, although glutamate-stimulated respiration was impaired. In contrast, the presence of L-lactate as an additional source protected against glutamate-induced neuronal death in control, but not ARALAR-deficient neurons.l-Lactate supplementation increased glutamate-stimulated respiration partially prevented the decrease in the cytosolic ATP/ADP ratio induced by glutamate and substantially diminished mitochondrial accumulation of 8-oxoguanosine, a marker of reactive oxygen species production, only in the presence, but not the absence, of ARALAR. In addition,l-lactate potentiated glutamate-induced increase in cytosolic Ca(2+), in a way independent of the presence of ARALAR. Interestingly,in vivo, the loss of half-a-dose of ARALAR in aralar(+/-)mice enhanced kainic acid-induced seizures and neuronal damage with respect to control animals, in a model of excitotoxicity in which increased L-lactate levels and L-lactate consumption have been previously proven. These results suggest that,in vivo, an inefficient operation of the shuttle in the aralar hemizygous mice prevents the protective role of L-lactate on glutamate excitotoxiciy and that the entry and oxidation of L-lactate through ARALAR-MAS pathway is required for its neuroprotective function.

SIGNIFICANCE STATEMENT

Lactate now stands as a metabolite necessary for multiple functions in the brain and is an alternative energy source during excitotoxic brain injury. Here we find that the absence of a functional malate-aspartate NADH shuttle caused by aralar/AGC1 disruption causes a block in lactate utilization by neurons, which prevents the protective role of lactate on excitotoxicity, but not glutamate excitotoxicity itself. Thus, failure to use lactate is detrimental and is possibly responsible for the exacerbated in vivo excitotoxicity in aralar(+/-)mice.

Reactive Oxygen Species: Physiological and Physiopathological Effects on Synaptic Plasticity

In the mammalian central nervous system, reactive oxygen species (ROS) generation is counterbalanced by antioxidant defenses. When large amounts of ROS accumulate, antioxidant mechanisms become overwhelmed and oxidative cellular stress may occur. Therefore, ROS are typically characterized as toxic molecules, oxidizing membrane lipids, changing the conformation of proteins, damaging nucleic acids, and causing deficits in synaptic plasticity. High ROS concentrations are associated with a decline in cognitive functions, as observed in some neurodegenerative disorders and age-dependent decay of neuroplasticity. Nevertheless, controlled ROS production provides the optimal redox state for the activation of transductional pathways involved in synaptic changes. Since ROS may regulate neuronal activity and elicit negative effects at the same time, the distinction between beneficial and deleterious consequences is unclear. In this regard, this review assesses current research and describes the main sources of ROS in neurons, specifying their involvement in synaptic plasticity and distinguishing between physiological and pathological processes implicated.

Cargo proteins of plasma astrocyte-derived exosomes in Alzheimer's disease

Efficient intercellular transfer of RNAs, proteins, and lipids as protected exosomal cargo has been demonstrated in the CNS, but distinct physiologic and pathologic roles have not been well defined for this pathway. The capacity to isolate immunochemically human plasma neuron-derived exosomes (NDEs), containing neuron-specific cargo, has permitted characterization of CNS-derived exosomes in living humans. Constituents of the amyloid β-peptide (Aβ)42-generating system now are examined in 2 distinct sets of human neural cells by quantification in astrocyte-derived exosomes (ADEs) and NDEs, enriched separately from plasmas of patients with Alzheimer's disease (AD) or frontotemporal dementia (FTD) and matched cognitively normal controls. ADE levels of β-site amyloid precursor protein-cleaving enzyme 1 (BACE-1), γ-secretase, soluble Aβ42, soluble amyloid precursor protein (sAPP)β, sAPPα, glial-derived neurotrophic factor (GDNF), P-T181-tau, and P-S396-tau were significantly (3- to 20-fold) higher than levels in NDEs for patients and controls. BACE-1 levels also were a mean of 7-fold higher in ADEs than in NDEs from cultured rat type-specific neural cells. Levels of BACE-1 and sAPPβ were significantly higher and of GDNF significantly lower in ADEs of patients with AD than in those of controls, but not significantly different in patients with FTD than in controls. Abundant proteins of the Aβ42 peptide-generating system in ADEs may sustain levels in neurons. ADE cargo proteins may be useful for studies of mechanisms of cellular interactions and effects of BACE-1 inhibitors in AD.-Goetzl, E. J., Mustapic, M., Kapogiannis, D., Eitan, E., Lobach, I. V., Goetzl, L., Schwartz, J. B., Miller, B. L. Cargo proteins of plasma astrocyte-derived exosomes in Alzheimer's disease.

Berberine Preconditioning Protects Neurons Against Ischemia via Sphingosine-1-Phosphate and Hypoxia-Inducible Factor-1α

Berberine exerts neuroprotective and modulates hypoxia inducible factor-1-alpha (HIF-1[Formula: see text]. Based on the role of HIF-1[Formula: see text] in hypoxia preconditioning and association between HIF-1[Formula: see text] and sphingosine-1-phosphate (S1P), we hypothesized that berberine preconditioning (BP) would ameliorate the cerebral injury induced by ischemia through activating the system of HIF-1[Formula: see text] and S1P. Adult male rats with middle cerebral artery occlusion (MCAO) and rat primary cortical neurons treated with oxygen and glucose deprivation (OGD) with BP at 24[Formula: see text]h (40[Formula: see text]mg/kg) and 2[Formula: see text]h (10[Formula: see text][Formula: see text]mol/L), respectively, were used to determine the neuroprotective effects. The HIF-1[Formula: see text] accumulation, and S1P metabolism were assayed in the berberine-preconditioned neurons, and the HIF-1[Formula: see text]-mediated transcriptional modulation of sphingosine kinases (Sphk) 1 and 2 was analyzed using chromatin immunoprecipitation and real-time polymerase chain reaction. BP significantly prevented cerebral ischemic injury in the MCAO rats at 24[Formula: see text]h and 72[Formula: see text]h following ischemia/reperfusion. In OGD-treated neurons, BP enhanced HIF-1[Formula: see text] accumulation with activation of PI3K/Akt, and induced S1P production by activating Sphk2 via the promotion of HIF-1[Formula: see text]-mediated Sphk2 transcription. In conclusion, BP activated endogenous neuroprotective mechanisms associated with the S1P/HIF-1 pathway and helped protect neuronal cells against hypoxia/ischemia.

Genistein improves sensorimotor gating: Mechanisms related to its neuroprotective effects on the striatum

Huntington's disease (HD) is a neurodegenerative disorder, characterized by selective atrophy in the striatum, particularly the medium spiny GABAergic efferent neurons. This results in striatal sensorimotor gating deficits. Systemic administration of 3-nitropropionic acid (3-NPA) produces selective lesions mimicking those of HD. Males were found to be more susceptible to 3-NPA-induced neurotoxicity than females, suggesting neuroprotective effects of estrogens. Phytoestrogens, including genistein, are good estrogenic alternatives that keep their beneficial effects on non-reproductive organs and lack the potential hazardous side effects. The current study was designed to investigate the potential beneficial effects of genistein in 3-NPA-induced HD in ovariectomized rats. Results showed that 3-NPA (20 mg/kg) administration caused significant disruption of the rats' locomotor activity and prepulse inhibition. In addition, it decreased striatal ATP levels and increased oxidative stress, inflammatory and apoptotic markers with striatal focal hemorrhage and gliosis. Pretreatment with 17β-estradiol (2.5 mg/kg) or genistein (20 mg/kg) led to a significant improvement of behavioral parameters, increased ATP production, decreased oxidative stress, attenuated inflammation and apoptosis. Therefore, this study suggests potential neuroprotective effects of genistein in ovariectomized rats challenged with 3-NPA.

Gene Transfer of Brain-derived Neurotrophic Factor (BDNF) Prevents Neurodegeneration Triggered by FXN Deficiency

Friedreich's ataxia is a predominantly neurodegenerative disease caused by recessive mutations that produce a deficiency of frataxin (FXN). Here, we have used a herpesviral amplicon vector carrying a gene encoding for brain-derived neurotrophic factor (BDNF) to drive its overexpression in neuronal cells and test for its effect on FXN-deficient neurons both in culture and in the mouse cerebellum in vivo. Gene transfer of BDNF to primary cultures of mouse neurons prevents the apoptosis which is triggered by the knockdown of FXN gene expression. This neuroprotective effect of BDNF is also observed in vivo in a viral vector-based knockdown mouse cerebellar model. The injection of a lentiviral vector carrying a minigene encoding for a FXN-specific short hairpin ribonucleic acid (shRNA) into the mouse cerebellar cortex triggers a FXN deficit which is accompanied by significant apoptosis of granule neurons as well as loss of calbindin in Purkinje cells. These pathological changes are accompanied by a loss of motor coordination of mice as assayed by the rota-rod test. Coinjection of a herpesviral vector encoding for BDNF efficiently prevents both the development of cerebellar neuropathology and the ataxic phenotype. These data demonstrate the potential therapeutic usefulness of neurotrophins like BDNF to protect FXN-deficient neurons from degeneration.

Synaptic abnormalities of mice lacking toll-like receptor (TLR)-9

Motor, sensory, and autonomic abnormalities are reported for toll-like receptor 9 (TLR9) knock-out (KO) mice. However, a physiological role of TLR9 in the nervous system is largely unknown. Since altered synaptic transmission can contribute to sensory and motor abnormalities, we evaluated neuromuscular junction (NMJ) function and morphology of TLR9 KO mice. Triangularis sterni nerve-muscle preparations were dissected from TLR9 KO and age-matched control mice. Two-electrode voltage clamp of the motor endplate revealed that the amplitude and frequency of miniature end plate currents (mEPCs) for TLR9 KO NMJs were significantly greater than control. In contrast, mean endplate current (EPC, 1Hz) amplitude was equivalent to control. The ratio of mean EPC to mean mEPC amplitude indicated a decline of quantal content (m) for TLR9 KO NMJs. Furthermore, m declined more rapidly than control in response to 50-Hz stimulus trains. A rightward shift of the mEPC amplitude distribution suggested formation of vesicles containing larger amounts of acetylcholine (ACh). Staining with rhodamine α-bungarotoxin revealed a significant decline of endplate size in TLR9 KO mice. This alteration may result from ACh-induced decline of acetylcholine receptor (AChR) expression resulting from increased frequency and amplitude of mEPCs. At the same time, excessive spontaneous vesicular ACh release may initiate retrograde suppression of excitation-secretion coupling. These data suggest a novel role of TLR9 in the development of the NMJ.

Superoxide dismutase 1 and glutathione peroxidase 1 are involved in the protective effect of sulodexide on vascular endothelial cells exposed to oxygen-glucose deprivation

Sulodexide (SDX) is widely used in the treatment of both arterial and venous thrombotic disorders. In addition to its recognized antithrombotic action, SDX has endothelial protective potential, which is independent of the coagulation/fibrinolysis system. However, the detailed molecular mechanisms of the endothelioprotective action of the drug are still unresolved. The aim of the present study was to determine whether treatment with SDX at concentrations of 0.125-0.5 lipase releasing unit (LRU)/ml have on the expression and activity of antioxidant enzymes in ischemic endothelial cells and how these effects might be related to the antiapoptotic properties of SDX. In the present study, human umbilical vein endothelial cells (HUVECs) were subjected to ischemia-simulating conditions (combined oxygen and glucose deprivation, OGD) for 6h to determine the protective effects of SDX. SDX (0.25 and 0.5LRU/ml) in OGD significantly increased the cell viability and prevented mitochondrial depolarization in the HUVECs. Moreover, SDX protected the HUVECs against OGD-induced apoptosis. At concentrations of 0.25 and 0.5LRU/ml, the drug increased both superoxide dismutase 1 (SOD1) and glutathione peroxidase 1 (GPx1) mRNA/protein expression together with a significant attenuation of oxidative stress in ischemic HUVECs. Our findings also demonstrate that an increase in both SOD and GPx activity is involved in the protective effect of SDX on ischemic endothelial cells. Altogether, these results suggest that SDX has a positive effect on ischemia-induced endothelial damage because of its antioxidant and antiapoptotic properties.

Creatine protects against mitochondrial dysfunction associated with HIV-1 Tat-induced neuronal injury

HIV-1 infected individuals live longer but experience a prevalence rate of over 50% for HIV-1 associated neurocognitive disorders (HAND) for which no effective treatment is available. Viral and cellular factors secreted by HIV-1 infected cells lead to neuronal injury and HIV-1 Tat continues to be implicated in the pathogenesis of HAND. Here we tested the hypothesis that creatine protected against HIV-1 Tat-induced neuronal injury by preventing mitochondrial bioenergetic crisis and/or redox catastrophe. Creatine blocked HIV-1 Tat(1-72)-induced increases in neuron cell death and synaptic area loss. Creatine protected against HIV-1 Tat-induced decreases in ATP. Creatine and creatine plus HIV-1 Tat increased cellular levels of creatine, and creatine plus HIV-1 Tat further decreased ratios of phosphocreatine to creatine observed with creatine or HIV-1 Tat treatments alone. Additionally, creatine protected against HIV-1 Tat-induced mitochondrial hypopolarization and HIV-1 Tat-induced mitochondrial permeability transition pore opening. Thus, creatine may be a useful adjunctive therapy against HAND.

The mitochondrial uncoupler DNP triggers brain cell mTOR signaling network reprogramming and CREB pathway up-regulation

Mitochondrial metabolism is highly responsive to nutrient availability and ongoing activity in neuronal circuits. The molecular mechanisms by which brain cells respond to an increase in cellular energy expenditure are largely unknown. Mild mitochondrial uncoupling enhances cellular energy expenditure in mitochondria and can be induced with 2,4-dinitrophenol (DNP), a proton ionophore previously used for weight loss. We found that DNP treatment reduces mitochondrial membrane potential, increases intracellular Ca(2+) levels and reduces oxidative stress in cerebral cortical neurons. Gene expression profiling of the cerebral cortex of DNP-treated mice revealed reprogramming of signaling cascades that included suppression of the mammalian target of rapamycin (mTOR) and insulin--PI3K - MAPK pathways, and up-regulation of tuberous sclerosis complex 2, a negative regulator of mTOR. Genes encoding proteins involved in autophagy processes were up-regulated in response to DNP. CREB (cAMP-response element-binding protein) signaling, Arc and brain-derived neurotrophic factor, which play important roles in synaptic plasticity and adaptive cellular stress responses, were up-regulated in response to DNP, and DNP-treated mice exhibited improved performance in a test of learning and memory. Immunoblot analysis verified that key DNP-induced changes in gene expression resulted in corresponding changes at the protein level. Our findings suggest that mild mitochondrial uncoupling triggers an integrated signaling response in brain cells characterized by reprogramming of mTOR and insulin signaling, and up-regulation of pathways involved in adaptive stress responses, molecular waste disposal, and synaptic plasticity. Physiological bioenergetic challenges such as exercise and fasting can enhance neuroplasticity and protect neurons against injury and neurodegeneration. Here, we show that the mitochondrial uncoupling agent 2,4-dinitrophenol (DNP) elicits adaptive signaling responses in the cerebral cortex involving activation of Ca(2+) -CREB and autophagy pathways, and inhibition of mTOR and insulin signaling pathways. The molecular reprogramming induced by DNP, which is similar to that of exercise and fasting, is associated with improved learning and memory, suggesting potential therapeutic applications for DNP.

Frataxin knockdown in human astrocytes triggers cell death and the release of factors that cause neuronal toxicity

Friedreich's ataxia (FA) is a recessive, predominantly neurodegenerative disorder caused in most cases by mutations in the first intron of the frataxin (FXN) gene. This mutation drives the expansion of a homozygous GAA repeat that results in decreased levels of FXN transcription and frataxin protein. Frataxin (Fxn) is a ubiquitous mitochondrial protein involved in iron-sulfur cluster biogenesis, and a decrease in the levels of this protein is responsible for the symptoms observed in the disease. Although the pathological manifestations of FA are mainly observed in neurons of both the central and peripheral nervous system, it is not clear if changes in non-neuronal cells may also contribute to the pathogenesis of FA, as recently suggested for other neurodegenerative disorders. Therefore, the aims of this study were to generate and characterize a cell model of Fxn deficiency in human astrocytes (HAs) and to evaluate the possible involvement of non-cell autonomous processes in FA. To knockdown frataxin in vitro, we transduced HAs with a specific shRNA lentivirus (shRNA37), which produced a decrease in both frataxin mRNA and protein expression, along with mitochondrial superoxide production, and signs of p53-mediated cell cycle arrest and apoptotic cell death. To test for non-cell autonomous interactions we cultured wild-type mouse neurons in the presence of frataxin-deficient astrocyte conditioned medium, which provoked a delay in the maturation of these neurons, a decrease in neurite length and enhanced cell death. Our findings confirm a detrimental effect of frataxin silencing, not only for astrocytes, but also for neuron-glia interactions, underlining the need to take into account the role of non-cell autonomous processes in FA.

Dysfunction of the PI3K-Akt-GSK-3 pathway is a common feature in cell culture and in vivo models of prion disease

AIMS

Transmissible spongiform encephalopathies, also called prion diseases, are characterized by the cerebral accumulation of misfolded prion protein (PrP(SC) ) and subsequent neurodegeneration. However, despite considerable research effort, the molecular mechanisms underlying prion-induced neurodegeneration are poorly understood. Here, we explore the hypothesis that prions induce dysfunction of the PI3K/Akt/GSK-3 signalling pathway.

METHODS

We employed two parallel approaches. Using cell cultures derived from mouse primary neurones and from a human neuronal cell line, we identified common elements that were modified by the neurotoxic fragment of PrP(106-126) . These studies were then complemented by comparative analyses in a mouse model of prion infection.

RESULTS

The presence of a polymerized fragment of the prion protein (PrP(106-126) ) or of a prion strain altered PI3K-mediated signalling, as evidenced by Akt inhibition and GSK-3 activation. PI3K activation by the addition of insulin or the expression of a constitutively active Akt mutant restored normal levels of Akt and GSK-3 activity. These changes were correlated with a reduction in caspase activity and an increase in neuronal survival. Moreover, we found that activation of caspase 3, Erk and GSK-3 are common features of PrP(106-126) -mediated neurotoxicity in cellular systems and prion infection in the mouse cerebellum, while activation of caspase 12 and JNK was observed in cellular models.

CONCLUSIONS

Our findings in cell culture and in vivo models of prion disease demonstrate marked alterations to the PI3K/Akt/GSK-3 pathway and suggest that two additional pathways contribute to PrP-induced neurotoxicity as responsible of JNK and caspase 12 activation.

Axonally derived matrilin-2 induces proinflammatory responses that exacerbate autoimmune neuroinflammation

In patients with multiple sclerosis (MS) and mice with experimental autoimmune encephalomyelitis (EAE), inflammatory axonal injury is a major determinant of disability; however, the drivers of this injury are incompletely understood. Here, we used the EAE model and determined that the extracellular matrix protein matrilin-2 (MATN2) is an endogenous neuronal molecule that is regulated in association with inflammatory axonal injury. Compared with WT mice, mice harboring a deletion of Matn2 exhibited reduced disease severity and axon damage following induction of EAE. Evaluation of neuron-macrophage cocultures revealed that exogenous MATN2 specifically signals through TLR4 and directly induces expression of proinflammatory genes in macrophages, promoting axonal damage. Moreover, the MATN2-induced proinflammatory response was attenuated greatly in macrophages from Myd88 KO mice. Examination of brain sections from patients with MS revealed that MATN2 is expressed in lesions but not in normal-appearing white matter. Together, our results indicate that MATN2 is a deleterious endogenous neuroaxonal injury response signal that activates innate immune cells and could contribute to early axonal damage in CNS inflammatory diseases like MS.

Heat shock protein 60: an endogenous inducer of dopaminergic cell death in Parkinson disease

BACKGROUND

Increasing evidence suggests that inflammation associated with microglial cell activation in the substantia nigra (SN) of patients with Parkinson disease (PD) is not only a consequence of neuronal degeneration, but may actively sustain dopaminergic (DA) cell loss over time. We aimed to study whether the intracellular chaperone heat shock protein 60 (Hsp60) could serve as a signal of CNS injury for activation of microglial cells.

METHODS

Hsp60 mRNA expression in the mesencephalon and the striatum of C57/BL6 mice treated with MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and the Hsp60/TH mRNA ratios in the SN of PD patients and aged-matched subjects were measured. To further investigate a possible link between the neuronal Hsp60 response and PD-related cellular stress, Hsp60 immunoblot analysis and quantification in cell lysates from SH-SY5Y after treatment with 100 μM MPP+ (1-methyl-4-phenylpyridinium) at different time points (6, 12, 24 and 48 hours) compared to control cells were performed. Additional MTT and LDH assay were used. We next addressed the question as to whether Hsp60 influences the survival of TH+ neurons in mesencephalic neuron-glia cultures treated either with MPP+ (1 μM), hHsp60 (10 μg/ml) or a combination of both. Finally, we measured IL-1β, IL-6, TNF-α and NO-release by ELISA in primary microglial cell cultures following treatment with different hHsp60 preparations. Control cultures were exposed to LPS.

RESULTS

In the mesencephalon and striatum of mice treated with MPTP and also in the SN of PD patients, we found that Hsp60 mRNA was up-regulated. MPP+, the active metabolite of MPTP, also caused an increased expression and release of Hsp60 in the human dopaminergic cell line SH-SY5Y. Interestingly, in addition to being toxic to DA neurons in primary mesencephalic cultures, exogenous Hsp60 aggravated the effects of MPP+. Yet, although we demonstrated that Hsp60 specifically binds to microglial cells, it failed to stimulate the production of pro-inflammatory cytokines or NO by these cells.

CONCLUSIONS

Overall, our data suggest that Hsp60 is likely to participate in DA cell death in PD but via a mechanism unrelated to cytokine release.

The developmental regulation of glutamate receptor-mediated calcium signaling in primary cultured rat hippocampal neurons

We have studied the developmental changes of glutamate-induced calcium (Ca²⁺) response in primary cultured hippocampal neurons at three different stages of cultures, 3, 7-8, and 14-16 days in vitro (DIV), using fura-2 single-cell digital micro-fluorimetry. We found that glutamate-induced Ca²⁺ signaling was altered during development, and that two different ionotropic glutamate receptors, α-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors (AMPARs) and N-methyl-D-aspartate receptors (NMDARs), were differently involved in the modulation of calcium response at different stages of neuronal culture. In the stages of culture at 3 and 8 DIV, glutamate-induced Ca²⁺ influx was mostly because of AMPAR activation and subsequent opening of voltage-dependent calcium channels, as Ca²⁺ response can be largely reduced by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and by nifedipine. In the advanced culture (14-17 DIV), glutamate-induced Ca²⁺ response was less sensitive to 6-cyano-7-nitroquinoxaline-2,3-dione and nifedipine. Furthermore, AMPA-induced Ca²⁺ response increased in a time-dependent manner during the cultures of 3-8 DIV and then reduced in the advanced culture of 14-17 DIV. NMDA-induced Ca²⁺ influx increased in a time-dependent manner, with a marked increase in the advanced culture (14-17 DIV). These results suggest that glutamate-induced Ca²⁺ signaling switched from AMPA-voltage-dependent calcium channel to NMDA-calcium signaling during development.

Bifidobacterium longum alleviates dextran sulfate sodium-induced colitis by suppressing IL-17A response: involvement of intestinal epithelial costimulatory molecules

Although some bacterial strains show potential to prevent colitis, their mechanisms are not fully understood. Here, we investigated the anti-colitic mechanisms of Bifidobacterium longum subsp. infantis JCM 1222^T, focusing on the relationship between interleukin (IL)-17A secreting CD4⁺ T cells and intestinal epithelial costimulatory molecules in mice. Oral administration of JCM 1222^T to mice alleviated dextran sulfate sodium (DSS)-induced acute colitis. The expression of type 1 helper T (Th1)- and IL-17 producing helper T (Th17)-specific cytokines and transcriptional factors was suppressed by JCM 1222^T treatment. Intestinal epithelial cells (IECs) from colitic mice induced IL-17A production from CD4⁺ T cells in a cell-cell contact-dependent manner, and this was suppressed by oral treatment with JCM 1222^T. Using blocking antibodies for costimulatory molecules, we revealed that epithelial costimulatory molecules including CD80 and CD40, which were highly expressed in IECs from colitic mice, were involved in IEC-induced IL-17A response. Treatment of mice and intestinal epithelial cell line Colon-26 cells with JCM 1222^T decreased the expression of CD80 and CD40. Collectively, these data indicate that JCM 1222^T negatively regulate epithelial costimulatory molecules, and this effect might be attributed, at least in part, to suppression of IL-17A in DSS-induced colitis.

Mesenchymal stem cells from human umbilical cord express preferentially secreted factors related to neuroprotection, neurogenesis, and angiogenesis

Mesenchymal stem cells (MSCs) are promising tools for the treatment of diseases such as infarcted myocardia and strokes because of their ability to promote endogenous angiogenesis and neurogenesis via a variety of secreted factors. MSCs found in the Wharton’s jelly of the human umbilical cord are easily obtained and are capable of transplantation without rejection. We isolated MSCs from Wharton’s jelly and bone marrow (WJ-MSCs and BM-MSCs, respectively) and compared their secretomes. It was found that WJ-MSCs expressed more genes, especially secreted factors, involved in angiogenesis and neurogenesis. Functional validation showed that WJ-MSCs induced better neural differentiation and neural cell migration via a paracrine mechanism. Moreover, WJ-MSCs afforded better neuroprotection efficacy because they preferentially enhanced neuronal growth and reduced cell apoptotic death of primary cortical cells in an oxygen-glucose deprivation (OGD) culture model that mimics the acute ischemic stroke situation in humans. In terms of angiogenesis, WJ-MSCs induced better microvasculature formation and cell migration on co-cultured endothelial cells. Our results suggest that WJ-MSC, because of a unique secretome, is a better MSC source to promote in vivo neurorestoration and endothelium repair. This study provides a basis for the development of cell-based therapy and carrying out of follow-up mechanistic studies related to MSC biology.

Effects of mild cold shock (25°C) followed by warming up at 37°C on the cellular stress response

Temperature variations in cells, tissues and organs may occur in a number of circumstances. We report here that reducing temperature of cells in culture to 25°C for 5 days followed by a rewarming to 37°C affects cell biology and induces a cellular stress response. Cell proliferation was almost arrested during mild hypothermia and not restored upon returning to 37°C. The expression of cold shock genes, CIRBP and RBM3, was increased at 25°C and returned to basal level upon rewarming while that of heat shock protein HSP70 was inversely regulated. An activation of pro-apoptotic pathways was evidenced by FACS analysis and increased Bax/Bcl2 and BclX(S/L) ratios. Concomitant increased expression of the autophagosome-associated protein LC3II and AKT phosphorylation suggested a simultaneous activation of autophagy and pro-survival pathways. However, a large proportion of cells were dying 24 hours after rewarming. The occurrence of DNA damage was evidenced by the increased phosphorylation of p53 and H2AX, a hallmark of DNA breaks. The latter process, as well as apoptosis, was strongly reduced by the radical oxygen species (ROS) scavenger, N-acetylcysteine, indicating a causal relationship between ROS, DNA damage and cell death during mild cold shock and rewarming. These data bring new insights into the potential deleterious effects of mild hypothermia and rewarming used in various research and therapeutical fields.

Nicotinamide forestalls pathology and cognitive decline in Alzheimer mice: evidence for improved neuronal bioenergetics and autophagy procession

Impaired brain energy metabolism and oxidative stress are implicated in cognitive decline and the pathologic accumulations of amyloid β-peptide (Aβ) and hyperphosphorylated tau in Alzheimer's disease (AD). To determine whether improving brain energy metabolism will forestall disease progress in AD, the impact of the β-nicotinamide adenine dinucleotide precursor nicotinamide on brain cell mitochondrial function and macroautophagy, bioenergetics-related signaling, and cognitive performance were studied in cultured neurons and in a mouse model of AD. Oxidative stress resulted in decreased mitochondrial mass, mitochondrial degeneration, and autophagosome accumulation in neurons. Nicotinamide preserved mitochondrial integrity and autophagy function, and reduced neuronal vulnerability to oxidative/metabolic insults and Aβ toxicity. β-Nicotinamide adenine dinucleotide biosynthesis, autophagy, and phosphatidylinositol-3-kinase signaling were required for the neuroprotective action of nicotinamide. Treatment of 3xTgAD mice with nicotinamide for 8 months resulted in improved cognitive performance, and reduced Aβ and hyperphosphorylated tau pathologies in hippocampus and cerebral cortex. Nicotinamide treatment preserved mitochondrial integrity, and improved autophagy-lysosome procession by enhancing lysosome/autolysosome acidification to reduce autophagosome accumulation. Treatment of 3xTgAD mice with nicotinamide resulted in elevated levels of activated neuroplasticity-related kinases (protein kinase B [Akt] and extracellular signal-regulated kinases) and the transcription factor cyclic adenosine monophosphate (AMP) response element-binding protein in the hippocampus and cerebral cortex. Thus, nicotinamide suppresses AD pathology and cognitive decline in a mouse model of AD by a mechanism involving improved brain bioenergetics with preserved functionality of mitochondria and the autophagy system.

Chronic inhibition of glycogen synthase kinase-3 protects against rotenone-induced cell death in human neuron-like cells by increasing BDNF secretion

Mitochondrial dysfunction is a common feature of many neurodegenerative disorders. Likewise, activation of glycogen synthase kinase-3 (GSK-3) has been proposed to play an important role in neurodegeneration. This multifunctional protein kinase is involved in a number of cellular functions and we previously showed that chronic inhibition of GSK-3 protects neuronal cells against mitochondrial dysfunction-elicited cell death, through a mechanism involving increased glucose metabolism and the translocation of hexokinase II (HKII) to mitochondria. Here, we sought to gain deeper insight into the molecular basis of this neuroprotection. We found that chronic inhibition of GSK-3, either genetically or pharmacologically, elicited a marked increase in brain-derived neurotrophic factor (BDNF) secretion, which in turn conferred resistance to mitochondrial dysfunction through subcellular re-distribution of HKII. These results define a molecular pathway through which chronic inhibition of GSK-3 may protect neuronal cells from death. Moreover, they highlight the potential benefits of enhanced neurotrophic factor secretion as a therapeutic approach to treat neurodegenerative diseases.

Neuroprotective effect of an angiotensin receptor type 2 agonist following cerebral ischemia in vitro and in vivo

Background

Intracerebral administration of the angiotensin II type 2 receptor (AT₂R) agonist, CGP42112, is neuroprotective in a rat model of ischemic stroke. To explore further its possible cellular target(s) and therapeutic utility, we firstly examined whether CGP42112 may exert direct protective effects on primary neurons following glucose deprivation in vitro. Secondly, we tested whether CGP42112 is effective when administered systemically in a mouse model of cerebral ischemia.

Methods

Primary cortical neurons were cultured from E17 C57Bl6 mouse embryos for 9 d, exposed to glucose deprivation for 24 h alone or with drug treatments, and percent cell survival assessed using trypan blue exclusion. Ischemic stroke was induced in adult male C57Bl6 mice by middle cerebral artery occlusion for 30 min, followed by reperfusion for 23.5 h. Neurological assessment was performed and then mice were euthanized and infarct and edema volume were analysed.

Results

During glucose deprivation, CGP42112 (1x10^-8 M and 1x10^-7 M) reduced cell death by ~30%, an effect that was prevented by the AT₂R antagonist, PD123319 (1x10^-6 M). Neuroprotection by CGP42112 was lost at a higher concentration (1x10^-6 M) but was unmasked by co-application with the AT₁R antagonist, candesartan (1x10^-7 M). By contrast, Compound 21 (1x10^-8 M to 1x10^-6 M), a second AT₂R agonist, had no effect on neuronal survival. Mice treated with CGP42112 (1 mg/kg i.p.) after cerebral ischemia had improved functional outcomes over vehicle-treated mice as well as reduced total and cortical infarct volumes.

Conclusions

These results indicate that CGP42112 can directly protect neurons from ischemia-like injury in vitro via activation of AT₂Rs, an effect opposed by AT₁R activation at high concentrations. Furthermore, systemic administration of CGP42112 can reduce functional deficits and infarct volume following cerebral ischemia in vivo.

Oxidative lipid modification of nicastrin enhances amyloidogenic γ-secretase activity in Alzheimer's disease

The cause of elevated level of amyloid β-peptide (Aβ42) in common late-onset sporadic [Alzheimer's disease (AD)] has not been established. Here, we show that the membrane lipid peroxidation product 4-hydroxynonenal (HNE) is associated with amyloid and neurodegenerative pathologies in AD and that it enhances γ-secretase activity and Aβ42 production in neurons. The γ-secretase substrate receptor, nicastrin, was found to be modified by HNE in cultured neurons and in brain specimens from patients with AD, in which HNE-nicastrin levels were found to be correlated with increased γ-secretase activity and Aβ plaque burden. Furthermore, HNE modification of nicastrin enhanced its binding to the γ-secretase substrate, amyloid precursor protein (APP) C99. In addition, the stimulation of γ-secretase activity and Aβ42 production by HNE were blocked by an HNE-scavenging histidine analog in a 3xTgAD mouse model of AD. These findings suggest a specific molecular mechanism by which oxidative stress increases Aβ42 production in AD and identify HNE as a novel therapeutic target upstream of the γ-secretase cleavage of APP.

Neuroprotective effects of L-carnitine against oxygen-glucose deprivation in rat primary cortical neurons

Purpose

Hypoxic-ischemic encephalopathy is an important cause of neonatal mortality, as this brain injury disrupts normal mitochondrial respiratory activity. Carnitine plays an essential role in mitochondrial fatty acid transport and modulates excess acyl coenzyme A levels. In this study, we investigated whether treatment of primary cultures of rat cortical neurons with L-carnitine was able to prevent neurotoxicity resulting from oxygen-glucose deprivation (OGD).

Methods

Cortical neurons were prepared from Sprague-Dawley rat embryos. L-Carnitine was applied to cultures just prior to OGD and subsequent reoxygenation. The numbers of cells that stained with acridine orange (AO) and propidium iodide (PI) were counted, and lactate dehydrogenase (LDH) activity and reactive oxygen species (ROS) levels were measured. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and the terminal uridine deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assay were performed to evaluate the effect of L-carnitine (1 µM, 10 µM, and 100 µM) on OGD-induced neurotoxicity.

Results

Treatment of primary cultures of rat cortical neurons with L-carnitine significantly reduced cell necrosis and prevented apoptosis after OGD. L-Carnitine application significantly reduced the number of cells that died, as assessed by the PI/AO ratio, and also reduced ROS release in the OGD groups treated with 10 µM and 100 µM of L-carnitine compared with the untreated OGD group (P<0.05). The application of L-carnitine at 100 µM significantly decreased cytotoxicity, LDH release, and inhibited apoptosis compared to the untreated OGD group (P<0.05).

Conclusion

L-Carnitine has neuroprotective benefits against OGD in rat primary cortical neurons in vitro.

Mitochondrion-derived reactive oxygen species lead to enhanced amyloid beta formation

AIMS

Intracellular amyloid beta (Aβ) oligomers and extracellular Aβ plaques are key players in the progression of sporadic Alzheimer's disease (AD). Still, the molecular signals triggering Aβ production are largely unclear. We asked whether mitochondrion-derived reactive oxygen species (ROS) are sufficient to increase Aβ generation and thereby initiate a vicious cycle further impairing mitochondrial function.

RESULTS

Complex I and III dysfunction was induced in a cell model using the respiratory inhibitors rotenone and antimycin, resulting in mitochondrial dysfunction and enhanced ROS levels. Both treatments lead to elevated levels of Aβ. Presence of an antioxidant rescued mitochondrial function and reduced formation of Aβ, demonstrating that the observed effects depended on ROS. Conversely, cells overproducing Aβ showed impairment of mitochondrial function such as comprised mitochondrial respiration, strongly altered morphology, and reduced intracellular mobility of mitochondria. Again, the capability of these cells to generate Aβ was partly reduced by an antioxidant, indicating that Aβ formation was also ROS dependent. Moreover, mice with a genetic defect in complex I, or AD mice treated with a complex I inhibitor, showed enhanced Aβ levels in vivo.

INNOVATION

We show for the first time that mitochondrion-derived ROS are sufficient to trigger Aβ production in vitro and in vivo.

CONCLUSION

Several lines of evidence show that mitochondrion-derived ROS result in enhanced amyloidogenic amyloid precursor protein processing, and that Aβ itself leads to mitochondrial dysfunction and increased ROS levels. We propose that starting from mitochondrial dysfunction a vicious cycle is triggered that contributes to the pathogenesis of sporadic AD.

Generation of complement component C5a by ischemic neurons promotes neuronal apoptosis

C5a receptors are found in the central nervous system (CNS), on both neurons and glia. However, the origin of the C5a, which activates these receptors, is unclear. In the present study, we show that primary cultured mouse cortical neurons constitutively express C5, the precursor of C5a, and express the classical receptor for C5a, CD88. With cell ischemia caused by 12 h glucose deprivation, or oxygen-glucose deprivation (OGD), neurons demonstrated increased apoptosis, up-regulation of CD88, and increased levels of C5a in the media. Exogenous murine C5a (100 nM) added to the neuronal cultures resulted in apoptosis, without affecting cell necrosis. Pretreatment of the cells with the specific CD88 receptor antagonist PMX53 (100 nM) significantly blocked ischemia-induced apoptosis (∼50%), and neurons from CD88(-/-) mice were similarly protected. In a murine model of stroke, using middle cerebral artery occlusion (MCAO), we found that C5a levels in the brain increased; this also occurred in cerebral slice cultures exposed to OGD. CD88(-/-) mice subjected to MCAO had significantly reduced infarct volumes and improved neurological scores. Taken together, our results demonstrate that neurons in the CNS have the capability to generate C5a following ischemic stress, and this has the potential to activate their C5a receptors, with deleterious consequences.

Continuous hypoxia attenuates paraquat-induced cytotoxicity in the human A549 lung carcinoma cell line

Paraquat (1,1'-dimethyl-4,4'-bipyridinium dichloride; PQ), an effective and widely used herbicide, was commercially introduced in 1962. It is reduced by the electron donor NADPH, and then reduced PQ transfers the electrons to molecular oxygen, resulting in the production of reactive oxygen species (ROS), which are related to cellular toxicity. However, the influence of continuous hypoxia on PQ-induced ROS production has not fully been investigated. We evaluated in vitro the protective effect of continuous hypoxia on PQ-induced cytotoxicity in the human carcinogenic alveolar basal epithelial cell line (A549 cells) by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay and live and dead assay, and by measuring lactate dehydrogenase (LDH) release. To elucidate the mechanism underlying this effect, we monitored the immunofluorescence of intracellular ROS and measured malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GPx) activities. Continuous hypoxia protected the A549 cells from PQ-induced cytotoxicity. Continuous hypoxia for a period of 24 h significantly reduced intracellular ROS, decreased MDA concentration in the supernatant, and normalized SOD and GPx activities. Continuous hypoxia attenuated PQ-induced cell toxicity in A549 cells. This protective effect might be attributable to the suppression of PQ-induced ROS generation.

Subtle cytotoxicity and genotoxicity differences in superparamagnetic iron oxide nanoparticles coated with various functional groups

Superparamagnetic iron oxide nanoparticles (SPIONs) have been widely utilized for the diagnosis and therapy of specific diseases, as magnetic resonance imaging (MRI) contrast agents and drug-delivery carriers, due to their easy transportation to targeted areas by an external magnetic field. For such biomedical applications, SPIONs must have multifunctional characteristics, including optimized size and modified surface. However, the biofunctionality and biocompatibility of SPIONs with various surface functional groups of different sizes have yet to be elucidated clearly. Therefore, it is important to carefully monitor the cytotoxicity and genotoxicity of SPIONs that are surfaced-modified with various functional groups of different sizes. In this study, we evaluated SPIONs with diameters of approximately 10 nm and 100~150 nm, containing different surface functional groups. SPIONs were covered with −O⁻ groups, so-called bare SPIONs. Following this, they were modified with three different functional groups – hydroxyl (−OH), carboxylic (−COOH), and amine (−NH₂) groups – by coating their surfaces with tetraethyl orthosilicate (TEOS), (3-aminopropyl)trimethoxysilane (APTMS), TEOS-APTMS, or citrate, which imparted different surface charges and sizes to the particles. The effects of SPIONs coated with these functional groups on mitochondrial activity, intracellular accumulation of reactive oxygen species, membrane integrity, and DNA stability in L-929 fibroblasts were determined by water-soluble tetrazolium, 2′,7′-dichlorodihydrofluorescein, lactate dehydrogenase, and comet assays, respectively. Our toxicological observations suggest that the functional groups and sizes of SPIONs are critical determinants of cellular responses, degrees of cytotoxicity and genotoxicity, and potential mechanisms of toxicity. Nanoparticles with various surface modifications and of different sizes induced slight, but possibly meaningful, changes in cell cytotoxicity and genotoxicity, which would be significantly valuable in further studies of bioconjugation and cell interaction for drug delivery, cell culture, and cancer-targeting applications.

The unsolved puzzle of neuropathogenesis in glutaric aciduria type I

Glutaric aciduria type I (GA-I) is a cerebral organic aciduria caused by deficiency of glutaryl-Co-A dehydrogenase (GCDH). GCDH deficiency leads to accumulation of glutaric acid (GA) and 3-hydroxyglutaric acid (3-OHGA), two metabolites that are believed to be neurotoxic, in brain and body fluids. The disorder usually becomes clinically manifest during a catabolic state (e.g. intercurrent illness) with an acute encephalopathic crisis that results in striatal necrosis and in a permanent dystonic-dyskinetic movement disorder. The results of numerous in vitro and in vivo studies have pointed to three main mechanisms involved in the metabolite-mediated neuronal damage: excitotoxicity, impairment of energy metabolism and oxidative stress. There is evidence that during a metabolic crisis GA and its metabolites are produced endogenously in the CNS and accumulate because of limiting transport mechanisms across the blood-brain barrier. Despite extensive experimental work, the relative contribution of the proposed pathogenic mechanisms remains unclear and specific therapeutic approaches have yet to be developed. Here, we review the experimental evidence and try to delineate possible pathogenetic models and approaches for future studies.

Translating promising preclinical neuroprotective therapies to human stroke trials

Stroke is the third leading cause of mortality and carries the greatest socioeconomic burden of disease in North America. Despite several promising therapies discovered in the preclinical setting, there have been no positive results in human stroke clinical trials to date. In this article, we review the potential causes for failure and discuss strategies that have been proposed to overcome the barrier to translation of stroke therapies. To improve the chance of success in future human stroke trials, we propose that therapies be tested in stroke models that closely resemble the human condition with molecular, imaging and functional outcomes that relate to outcomes utilized in clinical trials. These strategies include higher-order, old-world, nonhuman primate models of stroke with clinically relevant outcome measures. Although stroke neuroprotection has been looked upon pessimistically given the many failures in clinical trials to date, we propose that neuroprotection in humans is feasible and will be realized with rigorous translational science.

Up-regulation of A-type potassium currents protects neurons against cerebral ischemia

Excitotoxicity is the major cause of many neurologic disorders including stroke. Potassium currents modulate neuronal excitability and therefore influence the pathological process. A-type potassium current (I(A)) is one of the major voltage-dependent potassium currents, yet its roles in excitotoxic cell death are not well understood. We report that, following ischemic insults, the I(A) increases significantly in large aspiny (LA) neurons but not medium spiny (MS) neurons in the striatum, which correlates with the higher resistance of LA neurons to ischemia. Activation of protein kinase Cα increases I(A) in LA neurons after ischemia. Cultured neurons from transgenic mice lacking both Kv1.4 and Kv4.2 subunits exhibit an increased vulnerability to ischemic insults. Increase of I(A) by recombinant expression of Kv1.4 or Kv4.2 is sufficient in improving the survival of MS neurons against ischemic insults both in vitro and in vivo. These results, taken together, provide compelling evidence for a protective role of I(A) against ischemia.

Luteolin protects against reactive oxygen species-mediated cell death induced by zinc toxicity via the PI3K-Akt-NF-κB-ERK-dependent pathway

Zinc ion elevation contributes to acute excitotoxic brain injury and correlates with the severity of dementia in chronic neurodegenerative diseases. Downstream control of zinc-triggered signals is believed to be an efficient countermeasure. In the current study, we examined whether the flavonoid luteolin (Lu) could protect human neuroblastoma SH-SY5Y cells against zinc toxicity. We found that Lu suppressed overproduction of reactive oxygen species and protected against apoptotic cell death induced by zinc. By using specific inhibitors, we found that zinc strongly triggered Akt and ERK1/2 activation via a PI3K-Akt-NF-κB-ERK1/2-dependent pathway. Furthermore, Lu completely blocked this activation. Our study strongly supports the hypothesis that Lu might protect SH-SY5Y cells against ROS-mediated apoptotic cell death induced by zinc in part by inhibiting the PI3K-Akt-NF-κB-ERKs pathway.

Silencing of frataxin gene expression triggers p53-dependent apoptosis in human neuron-like cells

Friedreich's ataxia (FRDA) is an autosomal recessive disease caused by mutations that produce a deficiency in frataxin. Despite the importance of neurodegeneration in FRDA, little is known about the consequences of frataxin deficiency in neuronal cells. Here we describe a neuronal cell model for FRDA based on the use of lentiviral vectors that carry minigenes encoding frataxin-specific shRNAs that silence the expression of this gene. These lentivectors can knockdown frataxin expression in human neuroblastoma SH-SY5Y cells, which results in large-scale cell death in differentiated neuron-like cells but not in undifferentiated neuroblastoma cells. Frataxin-deficient neuron-like cells appear to die through apoptosis that is accompanied by up-regulation of p53, PUMA and Bax and activation of caspase-3. No significant autophagy is observed in frataxin-deficient neuron-like cells and the pharmacological activation of autophagy does not significantly increase neuronal cell death in response to the frataxin deficiency. Cell death triggered by frataxin knockdown can be impaired by interference with p53, caspase inhibitors and gene transfer of FXN. These results suggest that frataxin gene silencing in human neuron-like cells may constitute a useful cell model to characterize the molecular changes triggered by frataxin deficiency in neurons, as well as to search for therapies that may protect against neurodegeneration.